A conventional air-conditioning apparatus, such as a multi-air-conditioning apparatus for office buildings, performs a cooling operation or a heating operation by, for example, circulating a refrigerant between an outdoor unit, which is a heat source unit disposed outdoors, and indoor units disposed indoors. Specifically, conditioned spaces are cooled with the air that has been cooled by the refrigerant removing heat from the air and is heated with the air that has been heated by the refrigerant transferring its heat. For example, HFC (hydrofluorocarbon)-based refrigerants are typically used as the refrigerant for such an air-conditioning apparatus. In some proposals, natural refrigerants such as carbon dioxide (CO2) are used.
Meanwhile, there is an air-conditioning apparatus having a different configuration represented by a chiller system. Such an air-conditioning apparatus performs cooling or heating as follows. Cooling energy or heating energy is generated in a heat source unit disposed outdoors. A heat medium such as water or antifreeze is heated or cooled by a heat exchanger disposed in the outdoor unit. The heat medium is conveyed to indoor units, such as fan coil units or panel heaters, disposed in space to be conditioned (see Patent Literature 1, for example).
Moreover, there is a heat source side heat exchanger called a heat recovery chiller that connects a heat source unit to each indoor unit with four water pipes arranged therebetween and supplies cooled and heated water or the like simultaneously so that cooling or heating can be freely selected in indoor units (see Patent Literature 2, for example).
In addition, there is another air-conditioning apparatus that disposes a heat exchanger for a primary refrigerant and a secondary refrigerant near each indoor unit and the secondary refrigerant is conveyed to the indoor unit (see Patent Literature 3, for example).
Furthermore, there is an air-conditioning apparatus that connects an outdoor unit to each branch unit including a heat exchanger with two pipes in which a secondary refrigerant is carried to the corresponding indoor unit (see Patent Literature 4, for example).
Moreover, air-conditioning apparatuses, such as a multi-air-conditioning apparatus for a building, include an air-conditioning apparatus in which a refrigerant is circulated from an outdoor unit to a relay unit and a heat medium, such as water, is circulated from the relay unit to each indoor unit to reduce conveyance power for the heat medium while circulating the heat medium, such as water, through the indoor unit (refer to Patent Literature 5, for example).